STUDY DESIGN A prospective case series of roller coaster ride-induced significant spinal injuries. OBJECTIVES To describe a cohort of significantly injured roller coaster riders and the likely levels of acceleration at which the injuries occurred. These data are compared with contemporary efforts to define a lower limit of acceleration below which no significant spinal injury is likely to occur. METHODS Injury incident records and emergency medical service records for the Rattler Roller Coaster in San Antonio, Texas were evaluated for a 19 month period in 1992-3. Medical records for the more significant injuries were also reviewed and the specific injuries were tabulated, along with the demographics of the cohort. RESULTS There were 932,000 riders of the Rattler roller coaster, estimated to represent between 300,000 and 600,000 individual riders. It is estimated that there were a total of 656 neck and back injuries during the study period, and 39 were considered significant by the study inclusion criteria. Seventy two percent of the injured subjects sustained a cervical disc injury (28 of 39), and 71% of these injuries were at C5-6 (15 HNP, 5 symptomatic disc bulges), while 54% were at C6-7 (11 HNP, 4 symptomatic disc bulges). In the lumbar spine, the most frequent injury was a symptomatic disc bulge (20% of the cohort), followed by vertebral body compression fracture (18%), and L4-5 or L5-S1 HNP (13%). Accelerometry testing of passengers and train cars indicated a peak of 4.5-5g of vertical or axial acceleration and 1.5g of lateral acceleration over approximately 100 msec (0.1 sec) on both. CONCLUSIONS The results of this study suggest that there is no established minimum threshold of significant spine injury, and that the greatest explanation for injury presence following traumatic loading of the spine is individual susceptibility to injury, an unpredictable variable.
BACKGROUND Numerous factors are believed to influence the risk for injury to the cervical spine in low speed automobile crashes. Several studies have indicated that rear impact crashes are associated with greater risk for injury and, perhaps, a worse prognosis. We sought to answer the question concerning the possible reasons for the disparity in risk between front vector crashes and rear vector crashes using human subject crash testing. MATERIALS AND METHODS Instrumented human subjects were placed in instrumented crash test vehicles. Occupant accelerations were recorded. Force and moment analysis were calculated. Vehicle acceleration and speed metrics were recorded. Volunteers were subjected to three rear impact crashes, two of which were conducted in the unaware mode, and one in the aware mode in which the subjects were allowed to brace for the impact. All variables were held constant between frontal and rear impact sequences except the relative roles of the two vehicles (e.g., striking or struck). Thus, the only variables with this crossover study design were the impact vectors. RESULTS Volunteers rated their subjective experiences in the rear impact crashes as markedly more traumatic or physically unpleasant than in the frontal crashes. When holding vehicle mass, crash speeds, occupant variables and their interactions constant, the acceleration of the subjects’ heads was nearly three times higher in rear impact crash vectors vs. frontals. The resulting occupant kinematics were more complex in the rear impact crash. Additionally, it appears that the mechanism of injury in whiplash may vary with occupant mass. CONCLUSIONS The results suggest that more attention should be given to crashworthiness in the rear impact crash vector. The small study size does not allow a high level of confidence in regards to our findings of differential forces and resulting kinematics, but our results were always consistent and the observed differences were quite large. To our knowledge, this is the first study to look specifically at differential effects of rear vs. frontal crashes at low speeds, holding all other variables constant.
Design synthesis, San Diego, California
The cost of whiplash injuries—both in dollars spent for medical care and disability, and in terms of human suffering—are quite high in westernized nations. This is of particular interest, both from a public health perspective and a general societal one, because the disorder is theoretically preventable: In the very least it can be minimized. This can be achieved with crash prevention strategies and improvements in vehicle safety design—especially with more effective seat back and head restraint systems. Toward the goal of developing a standard for safety research in this area, a neck injury criterion (NIC) was proposed by Boström et al. in 1996. This criterion considers the relative horizontal acceleration and velocity between the bottom (T1) and top (C1) of the cervical spine and has face validity based on current literature. However, the NIC has become almost universally accepted, yet has not been subjected to rigorous scientific investigation or validation in terms of its representativeness in human occupant injury. Such investigation should specifically consider, first, whether the NIC provides an adequate proxy for all potential neck injuries due to whiplash and, secondly, whether the proposed threshold value of 15 m2/s2 is representative of the potential for all types of acute injuries. Based on a review of recent literature, recent human volunteer crash tests by Wheeler et al. and the those of the Spine Research Institute of San Diego, and based on mathematical MADYMO analysis of real world crash pulse data, it appears that the threshold for all acute injury in the general population is likely to require a lowering of the originally proposed NIC value. Moreover, it may be necessary to consider other factors not currently defined with the NIC, such as global neck hyperextension and the negative portion of the NIC curve. The conclusions of this paper should be considered preliminary. Certainly, ongoing work will be necessary to investigate this further and further analysis of more onboard crash data will prove invaluable.